Cystic fibrosis is the most common, lethal, genetic disease among white children, affecting approximately 1 in 2000 live births. The disease is characterized by generalized dysfunction of the exocrine glands resulting in a clinical picture of recurrent pulmonary disease, digestive and nutritional problems secondary to pancreatic insufficiency, and elevated sweat electrolytes. Thus far, sweat chloride assays have been the single most common diagnostic test for cystic fibrosis. But this test is difficult to perform, poorly standardized, and lacks reliability and reproducibility. The objective of this contract is the development of a simple, accurate, and reproducible test for the diagnosis of cystic fibrosis based on the observation that levels of immunoreactive trypsin, a protein, in blood of neonates with cystic fibrosis are consistently higher than those in blood of normal healthy neonates. The feasibility of this project was demonstrated through work done under a Phase I. Under this Phase II Program, MRI will develop a clinically useful radioimmunoassay and enzyme immunoassay for immunocreative trypsin (IRT) in blood samples spotted on filter paper; and validate it on several thousand blood samples in collaboration with the University of Wisconsin Medical Center. It is hoped that this Program would provide simple and reliable tests for large scale screening of neonates for cystic fibrosis.